Technical Field
The present disclosure relates to a displacement sensor using a spectroscope, a spectral characteristic measuring apparatus, a color measuring apparatus and a planar measured object quality monitoring apparatus to which the displacement sensor is applied, a displacement measuring method, a spectral characteristic measuring method, and a color measuring method.
Related Art
In a papermaking process, a film manufacturing process, etc., it is necessary to monitor a color of a manufactured object for quality management. For this purpose, a color measuring apparatus using a spectroscope is generally used. FIG. 12 is a diagram showing an external appearance of a planar measured object quality monitoring apparatus equipped with a color measuring apparatus using a spectroscope, and a case of measuring a color of paper to monitor quality of the paper will be described herein.
A planar measured object quality monitoring apparatus 600 includes a frame 610. Sheet-shaped paper 500 which is a measured object moves inside the frame 610 in a direction of arrow A by a roller (not shown) etc. An upper scanning head 620 for monitoring the paper 500 from the front side is movably attached to an upper side beam of the frame 610. A lower scanning head 630 for monitoring the paper 500 from the back side is movably attached to a lower side beam of the frame 610. The upper scanning head 620 and the lower scanning head 630 are constructed so as to reciprocate in a direction orthogonal to a paper movement direction in synchronization and monitor the same region from the front and the back.
A color measuring apparatus is mounted in, for example, the upper scanning head 620. Measurement points of the color measuring apparatus draw a locus as shown by a W-shaped line 501 by conveyance of the paper 500 and movement of the upper scanning head 620.
FIG. 13 is a diagram showing a structure of a color measuring apparatus using a spectroscope. As shown in FIG. 13, a color measuring apparatus 30 includes a barrel-shaped mirror 430 formed in a rotationally symmetrical shape. A measuring window 440 is installed in a portion, which faces the paper 500 that is the measured object, of the barrel-shaped mirror 430, so that dust or dirt is prevented from being got in. Light emitted in a xenon lamp 410 enters the barrel-shaped mirror 430 through a UV filter 420.
In order to obtain a stable measured result without being influenced by orientation characteristics of the measured object, it is important that the applied light should be rotationally symmetrical about a perpendicular of a measurement region M of the paper 500. Because of this, the measurement region M and the xenon lamp 410 which is a light source are arranged on the rotation axis of the barrel-shaped mirror 430.
The light reflected by the measurement region M is reflected by a mirror 450 installed on the rotation axis of the barrel-shaped mirror 430, and enters an optical fiber 320 through a collective lens 310. The reflected light guided to the optical fiber 320 is captured in a body of a spectroscope 300, and a luminous flux is limited by an entrance slit 330.
Thereafter, the light becomes parallel light by a parallel lens (an incoming side collimator lens) 340, and is applied to a diffraction device (a diffraction grating, a grating) 350. The light applied to the diffraction device 350 is reflected in a different direction according to a wavelength. When this light is collected by an integrating lens (an outgoing side collimator lens) 360, an image is formed in a different position every wavelength.
A line detector 370 constructed of plural photoelectric conversion elements arranged linearly is arranged in an image formation position, and detects intensity of light in each position. Since the position corresponds to a wavelength, spectral distribution which is intensity distribution every wavelength of the reflected light can be acquired based on a detected result of the line detector 370.
An operation module 400 controls measurement of the spectral distribution and also, converts the spectral distribution into an electrical signal to numerically process a color.
In the case of numerically processing the color, tristimulus values expressed by [Mathematical Formula 1] are widely used as a representation method of the color.
                    {                                                            X                =                                  k                  ⁢                                                            ∑                      400                      700                                        ⁢                                                                  S                        ⁡                                                  (                          λ                          )                                                                    ⁢                                                                        x                          _                                                ⁡                                                  (                          λ                          )                                                                    ⁢                                              R                        ⁡                                                  (                          λ                          )                                                                    ⁢                      Δ                      ⁢                                                                                          ⁢                      λ                                                                                                                                              Y                =                                  k                  ⁢                                                            ∑                      400                      700                                        ⁢                                                                  S                        ⁡                                                  (                          λ                          )                                                                    ⁢                                                                        y                          _                                                ⁡                                                  (                          λ                          )                                                                    ⁢                                              R                        ⁡                                                  (                          λ                          )                                                                    ⁢                      Δ                      ⁢                                                                                          ⁢                      λ                                                                                                                                              Z                =                                  k                  ⁢                                                            ∑                      400                      700                                        ⁢                                                                  S                        ⁡                                                  (                          λ                          )                                                                    ⁢                                                                        z                          _                                                ⁡                                                  (                          λ                          )                                                                    ⁢                                              R                        ⁡                                                  (                          λ                          )                                                                    ⁢                      Δ                      ⁢                                                                                          ⁢                      λ                                                                                                                              [                  Mathematical          ⁢                                          ⁢          Formula          ⁢                                          ⁢          1                ]            
Here,
k is a fixed coefficient for defining an absolute value,
S(λ) is spectral distribution of a light source determined by standards,
x(λ), y(λ) and z(λ) are spectral sensitivities called color matching functions determined by standards (where x represents an x bar, and the same applies to y and z),
R(λ) is spectral reflectance of a measured object, and
Δλ is a wavelength interval used at the time of computation. In addition, λ changes in the range of wavelengths of visible light, and the range of wavelengths of visible light is set at 400 nm to 700 nm in [Mathematical Formula 1].
Since only R(λ) changes according to the measured object in [Mathematical Formula 1], measurement of the color is, that is, measurement of the spectral reflectance of the measured object. The spectral reflectance can be calculated based on spectral distribution obtained in measurement. The other parameters in [Mathematical Formula 1] are recorded on memory etc. in the operation module 400 and could be read out as necessary.
Since the spectral reflectance is a ratio of reflected light to irradiated light every wavelength, the quantity of the light irradiated toward the measurement region M becomes a standard when the spectral reflectance is calculated based on spectral distribution obtained in measurement. As a result, the quantity of the light irradiated toward the measurement region M is previously acquired using a standard whiteboard etc.
However, the barrel-shaped mirror 430 has characteristics in which the quantity of light changes by a distance from the measured object in an optical axis direction. As a result, in order to maintain the quantity of the light irradiated toward the measurement region M constant, a distance between the upper scanning head 620 and the paper 500 must be maintained constant, a beam length in which the upper scanning head 620 moves is generally as long as several meters to 10 meters or more, and it is difficult to maintain a horizontal position constant. Also, it is difficult to maintain a horizontal position of the paper 500 conveyed by a roller etc. constant.
Hence, in order to accurately measure the spectral reflectance, for example, it is proposed that a relation between a change in spectral reflectance and displacement from a reference position is previously examined, and in a case of actually measuring the spectral reflectance, displacement between the upper scanning head 620 and the paper 500 is measured and the measured spectral reflectance is corrected.
In this case, for example, the color measuring apparatus 30 and a coil 621 are mounted in the upper scanning head 620, and air bearings 631 and a soft magnetic substance 632 are mounted in the lower scanning head 630 as shown in FIG. 14. The paper 500 which is the measured object is constructed so that a distance from the lower scanning head 630 is maintained constant by the air bearings 631. Also, since a distance the coil 621 and the soft magnetic substance 632 can be measured using a principle of electromagnetic induction, a distance between the upper scanning head 620 and the lower scanning head 630 can be obtained. Accordingly, a distance between the upper scanning head 620 and the paper 500 is calculated and the displacement from the reference position can be obtained, so that the spectral reflectance can be corrected.
Or, it is proposed that a change in the quantity of light with respect to variations in distance is decreased by using a cylindrical mirror or a tubular polygon mirror instead of the barrel-shaped mirror 430 in which the quantity of light changes by the distance.